Polycarbonate resins are superb in transparency, heat resistance, mechanical strength and the like, and so are widely used in electric, mechanical, automobile, medical and other applications. Especially, in the fields of sheet and film, use of polycarbonate resins is remarkably increasing for packaging materials, optical films, building materials and the like.
In these applications, heat resistance is often required. For example, for food packaging materials, which need to be hygienic, durability against a high temperature of 80° C. or higher used sterilization or filling is required. Also in the field of optical films, improvement in various characteristics is strong desired along with the recent development of flat panel displays including liquid crystal displays, plasma displays, organic EL displays and the like. Desired characteristics include high transparency and optical isotropy, and also heat resistance.
Polycarbonate sheets used for insert molding are required to have good size stability so as to be durable against expansion/shrinkage during and after heating, against wrinkles, and against warping of a molded product, as well as to have heat resistance. A polycarbonate resin production method, by which the rotation rate and the temperature of the take-up roll is controlled within a certain range at the time of melt-extrusion has been proposed (Japanese Laid-Open Patent Publication No. 2001-139705).
However, the above-mentioned production method has the following problems. When producing a sheet having a thickness of 0.5 to 2.0 mm, it is difficult to control the sheeting because, for example, the sheet is adsorbed to the roll due to a high temperature of the roll. In addition, a sheet produced by this method has a large expansion/shrinkage ratio when being heated, which results in a defect that, for example, the design is printed as shifted from the position originally intended. A sheet produced by this method also has a large warping ratio, and so is likely to cause the printing to be unacceptable when being used for name plates or the like in which printing is performed at a high processing speed. During the post-printing drying or transportation stage, such a sheet is largely warped, which declines the process work efficiency and also decreases the production yield.
Meanwhile, electrophotography technologies are widely used today for copiers, laser beam printers (hereinafter, referred to simply as “LBPs”), facsimile machines and the like owing to the high speed, high image quality and the like provided by such technologies.
Conventionally, as electrophotographic photosensitive bodies for the electrophotography technologies, inorganic-based photoconductive substances such as selenium, selenium/tellurium alloys, selenium/arsenic alloys, cadmium arsenide and the like are mainly used. However, recently, from the viewpoints of toxicity, safety, cost, productivity and the like, electrophotographic photosensitive bodies using organic photoconductive substances have been developed. In the case where an organic photoconductive substance has a low molecular weight, such an organic photoconductive substance is usually mixed with a binder resin to form a coating film. Substances used as the binder resin include, for example, vinyl polymers such as polymethylmethacrylate, polystyrene, poly(vinyl chloride) and the like, and copolymers thereof, and various thermoplastic and thermosetting resins such as polycarbonate, polyester, polysulfone, phenoxy resins, epoxy resins, silicone resins and the like. Electrophotographic photosensitive bodies using these binder resins can be easily formed into a thin film by a cast film production method, and thus are suitable to mass production and also are of relatively low cost. Among these various resins, polycarbonate resins have relatively good characteristics, and especially polycarbonate resins from 1,1-bis(4-hydroxyphenyl)cyclohexane are superb in abrasion resistance and electrophotographic characteristics and are used as binder resins (see Japanese Laid-Open Patent Publication No. 63-40159).
Meanwhile, electrophotographic photosensitive bodies provided with a hard coat on a surface thereof and thus having improved abrasion resistance are also developed. This type of electrophotographic photosensitive bodies have high abrasion resistance but the production process thereof is complicated and costly. Therefore, an electrophotographic photosensitive body having improved abrasion resistance and easily produced by the conventional production process is desired (see Japanese Laid-Open Patent Publication No. 2-216161).